[whswhs]

Here is what I would suggest for mecha. If you look at the weight statistics for humanoids, you can approximate human ST as 2 x (cube root off weight in pounds). But the formula for unliving entities is 4 x (cube root of weight in pounds). So I would give a human-sized "robot" twice human ST and HP, or typically 20.

The Growth advantage recommends minimum ST equal to 5 x height in yards. So for a mecha, I would go with 10 x height in yards. Pick an SM, check the height in yards, and multiply by 10. Example: We want a mecha that is SM +4; that's 10 yards, or 5 x human height. That gives it ST 100.

From this, you can get HP, weight, BL, and a basis for estimating occupancy and cargo (as Payload).

In approaching it this way, you're kind of building the mecha as a character. Of course you don't have to give it a full character sheet; just come up with the stats you need for the vehicle.